The invention relates to a method for measuring a parameter, in particular a temperature, of a molten bath, in particular a molten metal bath, by an optical fiber surrounded by a cover, the optical fiber being immersed in the molten bath and the radiation absorbed by the optical fiber in the molten bath being fed to a detector, wherein the optical fiber is heated when immersed in the molten bath. Furthermore, the invention relates to a device for measuring a parameter, in particular a temperature, of a molten bath, in particular a molten metal bath, with an optical fiber having a cover and a detector connected to the fiber, wherein the cover surrounds the fiber in a plurality of layers. Parameters in the sense of the invention may also be, for example, the height of the bath or the composition, in other words the proportion of components. It is also possible to measure in other molten baths, such as molten salt, cryolite or glass baths.
A method of this kind is known, for example, from Japanese patent application publication No. JP 11-118607. This describes how an optical fiber is used for measuring temperature in molten metal baths. The optical fiber is unwound from a spool and fed to the molten metal bath through a feed pipe. The radiation absorbed by the optical fiber is evaluated by a detector. Suitable optical fibers are known, for example, from Japanese patent application publication No JP 10-176954. The fiber described there is surrounded with a spacing by a metal tube. Arranged around the tube is a tube made of an insulating material, which in turn is surrounded by an outer metal tube. This structure prevents the inner metal tube from melting too quickly. The tube made of an insulating material contains carbon particles, so the inner metal tube does not melt until the corresponding tube portion is immersed in the molten metal bath. The fiber is immersed in the molten metal bath and tracked at a previously determined speed, so that it is possible to continue measuring, even if the tip of the fiber is destroyed. A similar optical fiber for measuring temperature is disclosed in Japanese patent application publication No JP 7-151918. Here, the optical fiber is surrounded by a protective metal tube surrounded by a layer of plastic material.
Furthermore, multi-layered wires are known, which are used in steelworks to introduce doping substances selectively into the molten steel bath (for example, in DE 199 16 235, DE 37 12 619, DE 196 23 194, U.S. Pat. No. 6,770,366).